Image reading apparatus

ABSTRACT

An image reading apparatus is provided which includes a cold-cathode tube as a light source for illuminating a document sheet, an inverter for providing the light source with driving power. A connection cable is used for electrically connecting the light source to the inverter. The image reading apparatus also includes three kinds of rows of light receiving elements arranged in the primary scanning direction for detecting the light reflected on the document sheet. A lens array is provided for focusing the reflected light at the respective rows of light receiving elements. The light receiving elements are mounted on a printed circuit board. The light source, the inverter, the lens array and the printed circuit board are supported by a single case of the image reading apparatus.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image reading apparatus. Moreparticularly, the present invention relates to a line image scanner foroptically reading a document sheet in full color. The present inventionalso relates to an image sensor chip advantageously used for such animage scanner.

2. Description of the Related Art

An example of conventional image reading apparatus is shown in FIG. 14of the accompanying drawings. The illustrated reading apparatus includesa light source unit Ba made up of a cold-cathode tube 1' and a mirror2'. The conventional apparatus also includes an inverter unit Bb forproviding driving power to the cold-cathode tube 1' via a flexible cable3', and a light leading unit Bc provided with mirrors 4a', 4b'. Theconventional apparatus further includes an image reading unit Bdprovided with a lens 5' and an image sensor 6'.

In operation, the light source unit Ba is reciprocated in the secondaryscanning direction under a stationary glass plate 7' on which a documentsheet K to be read out is placed. Accordingly, the light leading unit Bcis repeatedly moved in the secondary scanning direction.

The conventional image reading apparatus has been found to bedisadvantageous in the following points.

First, the light source unit Ba, the inverter unit Bb and the lightleading unit Bc are produced separately from each other. With such anarrangement, it is difficult to accurately position these units to eachother. Further, production costs tend to be high since a plurality ofseparate units need to be manufactured.

Still further, the flexible cable 3' connecting the light source unit Bato the inverter unit Bb is long enough, so that the reciprocatingmovement of the light source unit Ba is not hindered. However, as thelength of the flexible cable 3' increases, the loss of the driving powerprovided by the inverter unit Bb to the cold-cathode tube 1' increases.As a result, the luminance of the cold-cathode tube 17 may be undulyreduced.

The conventional image reading apparatus also has the followingdisadvantage.

Though not shown in FIG. 14, the image sensor 6' includes a plurality ofimage sensor chips. Each image sensor chip is formed with three rows oflight receiving elements extending in the primary scanning direction. Afirst row is made up of red light receiving elements used forselectively detecting a red component of white light. Similarly, asecond row is made up of green light receiving elements used forselectively detecting a green component of white light, while a thirdrow is made up of blue light receiving elements used for selectivelydetecting a blue component of white light.

Each row of light receiving elements has a pitch P between the lightreceiving elements in the primary scanning direction. The pitch betweenthe light receiving elements in the secondary scanning direction (whichis perpendicular to the primary scanning direction) is also P. As viewedin the secondary scanning direction, each of the light receivingelements has a length of P/2.

For providing color selectivity, color filters are used for the lightreceiving elements. Specifically, each red light receiving element iscovered by a red filter which allows selective permeation of red light,whereas each green light receiving element is covered by a green filterwhich allows selective permeation of green light. Similarly, each bluelight receiving element is covered by a blue filter which allowsselective permeation of blue light.

In the conventional image reading apparatus, no attention has been paidto e.g., the thickness of the color filters, and three types of colorfilters may have the same thickness. With such an arrangement, however,it may be impossible to realize a high-fidelity reproduction of the readimage. This is partly because properties of the color filters are notthe same for the different color lights (red, green, blue) and partlybecause properties of the light receiving elements are not the same forthe different color lights, either.

Specifically, as shown in FIG. 15, among the three colors (Red, Greenand Blue), a conventionally available light receiving element (e.g.,phototransistor) has the highest relative sensitivity for red, thesecond highest relative sensitivity for green, and the lowest relativesensitivity for blue.

FIG. 16 shows relationship between the wave length of incident light andthe transmittance of the respective color filters (Red filter, Greenfilter and Blue filter). As illustrated, the red filter has the highesttransmittance, while the green filter has the second highesttransmittance, and the blue filter has the lowest transmittance.

As shown in FIG. 17, a typical cold-cathode tube generates white lightwhose green component has the highest energy ratio compared with thoseof the red and blue components.

FIG. 18 shows the reflectivity of red (R), green (G) and blue (B) lightson four types of test charts (WHITE, RED, GREEN, BLUE and BLACK testcharts). As illustrated, of three colors, blue light is reflected moston the white test chart. Red light is reflected most on the red testchart, green light is reflected most on the green test chart, and bluelight is reflected most on the blue test chart. When the test chart isblack, the three color lights are hardly reflected.

FIG. 19 is obtained from a combination of FIG. 16 and FIG. 18. As isshown, when using the white test chart, the green light has the highestproduct of the transmittance and the reflectivity.

FIG. 20 is obtained from a combination of FIG. 15, FIG. 17 and FIG. 19.FIG. 20 shows the output voltages generated by the three types of lightreceiving elements (Red, Green and Blue) when the four types of testcharts (WHITE, RED, GREEN, BLUE and BLACK) are irradiated with whitelight. As is shown, when using the white test chart, the green lightreceiving element generates the highest output voltage. When using thered test chart, the red light receiving element generates the highestoutput voltage.

Still further, the conventional image reading apparatus isdisadvantageous in the following point.

Referring to FIG. 21, for performing image reading for one line, thelight receiving elements 8' (only one shown) of each image sensor chipare advanced by the distance P in the secondary scanning direction withrespect to the document sheet. During this movement, however, the lightreceiving element 8' scans a rectangular area having a length of (P+L).This means that image reading for each line is performed for an undulylarger area due to the length L of the light receiving element itself.As a result, with the use of the conventional image reading apparatus, ahigh-fidelity printout reproduction of the image carried by the documentsheet may not be realized.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide an imagereading apparatus capable of overcoming the disadvantages describedabove.

Another object of the present invention is to provide an image sensorchip advantageously incorporated in such an image reading apparatus.

According to a first aspect of the present invention, there is providedan image reading apparatus comprising:

a light source for irradiating a document sheet with light;

a power supplier for providing the light source with driving power;

a connection cable for electrically connecting the light source to thepower supplier;

at least one row of light receiving elements arranged in a primaryscanning direction for detecting the light reflected on the documentsheet;

a lens array for focusing the reflected light at the row of lightreceiving elements;

a printed circuit board for mounting the row of light receiving elementsthereon; and

a case for supporting the light source, the power supplier, the lensarray and the printed circuit board.

The image reading apparatus may further comprise a light reflectingholder formed with a groove for accommodating the light source. Theimage reading apparatus may also comprise a shield frame foraccommodating the light reflecting holder.

Preferably, the shield frame is grounded.

According to a preferred embodiment of the present invention, the caseis formed with a first hollow portion for accommodating the lightsource, a second hollow portion for accommodating the power supplier anda third hollow portion for accommodating the lens array. Further, thecase is formed with a cutout for causing the first and the second hollowportions to communicate with each other, the connection cable extendingthrough the cutout.

The light source may comprise a cold-cathode tube, and the powersupplier may comprise an inverter.

According to a second aspect of the present invention, there is providedan image reading apparatus comprising:

a light source for irradiating a document sheet with light;

a row of red light receiving elements arranged in a primary scanningdirection for detecting a red component of the light reflected on thedocument sheet, each red light receiving element having a length of L ina secondary scanning direction which is perpendicular to the primaryscanning direction;

a row of green light receiving elements arranged in the primary scanningdirection for detecting a green component of the reflected light, therow of green light receiving elements being displaced from the row ofred light receiving elements by a distance of P in the secondaryscanning direction, each green light receiving element having a lengthof L in the secondary scanning direction;

a row of blue light receiving elements arranged in the primary scanningdirection for detecting a blue component of the reflected light, the rowof blue light receiving elements being displaced from the row of greenlight receiving elements by a distance of P in the secondary scanningdirection, each blue light receiving element having a length of L in thesecondary scanning direction; and

a signal selector;

wherein, in performing image reading for one scanning line, the signalselector is arranged to adopt, as a necessary image signal, a voltagegenerated by each of the light receiving elements during a period whensaid each light receiving element is moved in the secondary scanningdirection relative to the document sheet by a first feed distance, thesignal selector being also arranged to disregard, as an unnecessaryimage signal, a voltage generated by said each light receiving elementduring a period when said each light receiving element is moved in thesecondary scanning direction relative to the document sheet by a secondfeed distance subsequent to the first feed distance.

The signal selector may be realized by a CPU, a gate array, or a PLA(programmable logic array).

The first feed distance may be equal to (P-L), and the second feeddistance may be equal to L.

Alternatively, the first feed distance may be smaller than (P-L), andthe second feed distance may be greater than L.

The light source may comprise a cold-cathode tube or a light-emittingdiode.

According to a third aspect of the present invention, there is providedan image reading apparatus comprising:

a light source for irradiating a document sheet with light;

a row of red light receiving elements arranged in a primary scanningdirection for detecting a red component of the light reflected on thedocument sheet, each red light receiving element having a length of L ina secondary scanning direction which is perpendicular to the primaryscanning direction;

a row of green light receiving elements arranged in the primary scanningdirection for detecting a green component of the reflected light, therow of green light receiving elements being displaced from the row ofred light receiving elements by a distance of P in the secondaryscanning direction, each green light receiving element having a lengthof L in the secondary scanning direction;

a row of blue light receiving elements arranged in the primary scanningdirection for detecting a blue component of the reflected light, the rowof blue light receiving elements being displaced from the row of greenlight receiving elements by a distance of P in the secondary scanningdirection, each blue light receiving element having a length of L in thesecondary scanning direction;

a light controller;

wherein, in performing image reading for one scanning line, the lightcontroller is arranged to turn on the light source during a period wheneach of the light receiving elements is moved in the secondary scanningdirection relative to the document sheet by a first feed distance, thelight controller being also arranged to turn off the light source duringa period when said each light receiving element is moved in thesecondary scanning direction relative to the document sheet by a secondfeed distance subsequent to the first feed distance.

The light controller may be realized by a CPU, a gate array or PLA.

The image reading apparatus may further comprise an output timingcontroller for regulating output of an image signal from each of thelight receiving elements, so that the image signal is output from saideach light receiving element when the light source is turned off.

According to a fourth aspect of the present invention, there is providedan image sensor chip comprising:

a chip substrate;

a row of red light receiving elements formed in the chip substrate andarranged in a first direction for detecting red light, each of the redlight receiving elements being covered by a red filter;

a row of green light receiving elements formed in the chip substrate andarranged in the first direction for detecting green light, each of thegreen light receiving elements being covered by a green filter; and

a row of blue light receiving elements formed in the chip substrate andarranged in the first direction for detecting blue light, each of theblue light receiving elements being covered by a blue filter;

wherein the red, green and blue filters have predetermined thicknesses,the thickness of the red filter being greater than the thickness of thegreen filter, the thickness of the green filter being greater than thethickness of the blue filter.

According to a fifth aspect of the present invention, there is providedan image sensor chip comprising:

a chip substrate;

a row of red light receiving elements formed in the chip substrate andarranged in a first direction for detecting red light, each of the redlight receiving elements having a red light receiving surface covered bya red filter;

a row of green light receiving elements formed in the chip substrate andarranged in the first direction for detecting green light, each of thegreen light receiving elements having a green light receiving surfacecovered by a green filter; and

a row of blue light receiving elements formed in the chip substrate andarranged in the first direction for detecting blue light, each of theblue light receiving elements having a blue light receiving surfacecovered by a blue filter;

wherein an area of the red light receiving surface is smaller than anarea of the green light receiving surface, the area of the green lightreceiving surface being smaller than an area of the blue light receivingsurface.

According to a sixth aspect of the present invention, there is providedan image sensor chip comprising:

a chip substrate;

a row of red light receiving elements formed in the chip substrate andarranged in a first direction for detecting red light, each of the redlight receiving elements being covered by a red filter;

a row of green light receiving elements formed in the chip substrate andarranged in the first direction for detecting green light, each of thegreen light receiving elements being covered by a green filter;

a row of blue light receiving elements formed in the chip substrate andarranged in the first direction for detecting blue light, each of theblue light receiving elements being covered by a blue filter;

a first amplifier for the row of red light receiving elements;

a second amplifier for the row of green light receiving elements; and

a third amplifier for the row of blue light receiving elements;

wherein an amplification factor of the first amplifier is smaller thanan amplification factor of the second amplifier, the amplificationfactor of the second amplifier being smaller than an amplificationfactor of the third amplifier.

Other features and advantages of the present invention should becomeclear from the detailed description to be made hereinafter referring tothe accompanied drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is an explosive view showing an image reading apparatus accordingto a first embodiment of the present invention;

FIG. 2 is an enlarged view schematically showing a principal portion ofthe image reading apparatus of FIG. 1;

FIG. 3 is a sectional view taken along lines III--III in FIG. 2;

FIG. 4 is a sectional view taken along lines IV--IV in FIG. 2;

FIG. 5 is an explosive view of the image reading apparatus of FIG. 1,showing how the apparatus is assembled;

FIG. 6 is a plan view showing an image sensor chip used for the imagereading apparatus of FIG. 1;

FIG. 7 is a sectional view taken along lines VII--VII in FIG. 6;

FIG. 8 is a plan view showing a modified arrangement of the image sensorchip of FIG. 6;

FIG. 9 is a block diagram showing a control system used for the imagereading apparatus of FIG. 1;

FIG. 10 illustrates output timing of image signals supplied from lightreceiving elements of the image sensor chip of FIG. 6;

FIG. 11 is a circuit diagram of the image sensor chip of FIG. 6;

FIG. 12 shows a modified version of a control system;

FIG. 13 illustrates a relationship between a paper feed and actuation ofa light source;

FIG. 14 illustrates a conventional image reading apparatus;

FIG. 15 shows a relationship between wave lengths of light and relativesensitivities of light receiving elements;

FIG. 16 shows a relationship between wave lengths of light andtransmittances of color filters;

FIG. 17 shows a relationship between wave lengths of light emitted froma cold-cathode tube and energy ratios of the same light;

FIG. 18 illustrates how well various test charts reflect light;

FIG. 19 shows variations of products of the filter transmittance and thetest chart reflectivity;

FIG. 20 shows variations of outputs from an image sensor chip; and

FIG. 21 illustrates the movement of a light receiving element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiments of the present invention will be specificallydescribed below with reference to the accompanying drawings.

Reference is first made to FIG. 1 which is an explosive view showingvarious components used for an image reading apparatus according to afirst embodiment of the present invention. The image reading apparatusof this embodiment is a flat-bed-type line image scanner A which mainlyincludes a case 1, a cold-cathode tube 2, an inverter 3, a circuit board4, a light reflecting holder 5, a shield frame 6, a lens array 7, and atransparent cover member 8.

In the illustrated embodiment, the case 1 is elongated in one direction(primary scanning direction N1 in FIG. 2) and has a box configurationfor accommodating the cold-cathode tube 2, the inverter 3, the lightreflecting holder 5, the shield frame 6 and the lens array 7. The case 1supports the cover member 8 mounted thereon from above. The case 1 alsosupports the circuit board 4 attached thereto from below. The case 1 maybe made of a synthetic resin for example.

The cold-cathode tube 2 having a light outlet surface 20 serves as awhite light source and extends in the primary scanning direction foruniformly irradiating a document sheet with white light over the entirewidth of the document sheet. In operation, driving power (for example,600V, 30-160 kHz, 3-5 mA) is applied across the cold-cathode tube 2. Ifnecessary or preferred, the cold-cathode tube 2 may be replaced by oneor more white LEDs.

The inverter 3 includes a circuit board 33 on which suitable circuits(not shown) are provided. The inverter 3 serves to convert low-voltagedirect current into alternating current of high-voltage andhigh-frequency. The non-illustrated circuits are covered by a cover case34. Preferably, the inverter 3 is provided with suitable means forpreventing noise generation in the circuits. The inverter 3 includes apower inlet portion 31 provided with two terminals 31a and 31b for inputof direct current from an external power source. As best shown in FIG.3, the circuit board 33 of the inverter 3 has a reverse surface providedwith a grounding layer 32 having a sufficiently large area. Thegrounding layer 32 is electrically connected to the above-mentionedterminal 31b. Output voltage of the inverter 3 is supplied to thecold-cathode tube 2 via two flexible cords 30a and 30b.

The circuit board 4 has an upper surface (inner surface with respect tothe case 1) for mounting an array of image sensor chips 40. Though notshown in FIG. 1, the upper surface of the circuit board 4 is formed witha wiring pattern. The details of each image sensor chip 40 will bedescribed hereinafter.

As shown in FIG. 1, the circuit board 4 is elongated in the primaryscanning direction, and the array of image sensor chips 40 extends inthe primary scanning direction. Further, as also shown in FIG. 1, thecircuit board 4 is provided with a connector 49 for establishingconnection with a n external circuit or unit.

The light reflecting holder 5 supports the cold-cathode tube 2 withinthe case 1 while efficiently reflecting white light toward the covermember 8 with a high reflectivity. Due to the provision of the lightreflecting holder 5, the white light generated by the cold-cathode tube2 is concentratively directed to a scanning position P (see FIG. 3) on aglass plate 9 as a strip or line extending in the primary scanningdirection.

For accommodating the cold-cathode tube 2, the light reflecting holder 5is provided with a groove 50 having an opening 51. The groove 50 has aninner surface 50a which is preferably white for effective lightreflection. The cross-sectional diameter of the groove 50 is larger thanthat of the cold-cathode tube 2 but equal to the outer diameters ofrubber rings 21 fixed around the ends of the cold-cathode tube 2. Suchan arrangement is advantageous in keeping the cold-cathode tube 2 awayfrom the light reflecting holder 5. In this way, heat generated by thecold-cathode tube 2 is prevented from dissipating through direct contactwith the light reflecting holder 5. As a result, the cold-cathode tube 2is kept at appropriate temperatures, thereby providing a sufficientamount of light needed for performing proper image reading.

As shown in FIGS. 3 and 4, the light reflecting holder 5 is providedwith a cutout 52 for accommodating the flexible cords 30a and 30b.

The shield frame 6, which may be prepared by pressworking a metal plate,is also elongated in the primary scanning direction. The shield frame 6,the cold-cathode tube 2 and the light reflecting holder 5 aresubstantially equal in length, as can be seen from FIG. 1. The shieldframe 6 has a rectangular cross section with its top side missing (seealso FIGS. 3 or 4). The shield frame 6 is provided with a cutout 61 forallowing passage of the flexible cords 30a-30b, and with a clip-liketerminal 62. The clip-like terminal 62, used for grounding purposes ofthe shield frame 6, may be prepared by simply bending an integralportion of the terminal 62.

As best shown in FIG. 5, the case 1 is formed with an upwardly openhollow portion 11 (first hollow portion) large enough to accommodate theshield frame 6. Thus, after the cold-cathode tube 2, the lightreflecting holder 5 and the shield frame 6 are put together, they areeasily accommodated together in the case 1 by simply being inserted intothe first hollow portion 11.

The case 1 is also formed with another upwardly open, hollow portion 12(second hollow portion) adjacent to the first hollow portion 11. Thesecond hollow portion 12 is used for accommodating the inverter 3. Asshown in FIG. 1, the two hollow portions 11-12 are communicated witheach other via a cutout 15 for allowing passage of the flexible cords30a-30b. The two hollow portions 11-12 are also communicated via anothercutout 16 for accommodating the clip-like terminal 62. As shown in FIG.3, the grounding layer 32 and the clip-like terminal 62 are held infacing relation to each other, establishing electrical connectiontherebetween.

The first and second hollow portions 11-12 are closed by the covermember 8. Thus, high-voltage portions of the inverter 3 accommodated inthe second hollow portion 12 will not be accidentally touched. However,as shown in FIG. 2, the power inlet portion 31 remains exposed to theexterior through a window 17 formed in a side surface of the case 1. Inthis arrangement, electric connection is readily established to theinverter 3 by inserting a plug 99 into the window 17.

The lens array 7 includes an array of selfoc lenses (self-focusinglenses) extending in the primary scanning direction. The lens array 7 ispositioned between the glass plate 9 and the array of image sensor chips40 for focusing the light reflected on a document sheet K onto the arrayof image sensor chips 40, thereby forming non-inverted, non-magnifiedimages read from the document sheet. As best shown in FIG. 5, the case 1is formed with another upwardly open, hollow portion 13 (third hollowportion) for accommodating the lens array 7.

The image sensor chips 40 are arranged to output image signals inaccordance with the luminous energies of the light reflected on thedocument sheet. The circuit board 4 may be made of a resin material suchas epoxy or ceramic material. As shown in FIG. 5, the case 1 is formedwith a downwardly open, fourth hollow portion 14 for accommodating thecircuit board 4.

In the illustrated embodiment, the inverter 3 is positioned close to thecold-cathode tube 2. With such an arrangement, the flexible cords30a-30b extending between the inverter 3 and the cold-cathode tube 2 canbe short accordingly. Thus, it is possible to reduce power loss alongthe flexible cords 30a-30b, and the amount of light generated by thecold-cathode tube 2 is advantageously increased.

As stated above, high-frequency driving power generated by the inverter3 is supplied to the cold-cathode tube 2 via the flexible cords 30a-30b.In this arrangement, high-frequency noises may unduly be emitted fromthe flexible cords 30a-30b and/or the cold-cathode tube 2. Withouttaking proper countermeasure, those noises may adversely affect imagesignals supplied from the image sensor chips 40, thereby making itimpossible to realize a high-fidelity printout reproduction of the readimage. In this regard, the image sensor chips 40 of the presentinvention are shielded from the cold-cathode tube 2 and the flexiblecords 30a-30b by the shield frame 6. Thus, the above-mentioned problemis overcome.

According to the present invention, as previously described, thecold-cathode tube 2, light reflecting holder 5 and shield frame 6 areput together, without using bolts or an adhesive for example. Further,it is possible to accommodate the assembly of the above-mentioned threeelements 2, 5, 6 within the case 1 by simply fitting it into the firsthollow portion 11. Similarly, it is possible to put the inverter 3 andthe lens arrays 7 into place within the case 1 by simply fitting theminto the hollow portions 12 and 13, respectively.

Reference is now made to FIG. 6. As illustrated, each of the imagesensor chips 40, which is rectangular in plan view, comprises a chipsubstrate carrying plural rows NR, NG, NB of light receiving elements41R, 41G, 41B. Each of the rows NR, NG, NB extends in the primaryscanning direction N1, and the respective rows include a different kindof light receiving elements in identical number and arrangement.According to the illustrated embodiment, specifically, the image sensorchip 40 comprises a first row NR of red light receiving elements 41R, asecond row NG of green light receiving elements 41G, and a third row NBof blue light receiving elements 41B, arranged in the mentioned order inthe secondary scanning direction N2. Thus, the second row NG of greenlight receiving elements 41G is interposed between the first row NR ofred light receiving elements 41R and the third row NB of blue lightreceiving elements 41B.

As appreciated from FIG. 1, each of the image sensor chips 40 is mountedon the circuit board 4 with its longitudinal axis extending in theprimary scanning direction. Therefore, each row NR, NG, NB of lightreceiving elements 41R, 41G, 41B of each image sensor chip 40 is alignedwith a corresponding row of light receiving elements of any other imagesensor chip with respect to the secondary scanning direction. Forenabling the respective image sensor chips 40 to be positionedaccurately on the circuit board 4, each of the image sensor chips 40 maybe formed with a positional reference mark (not shown). The number ofthe image sensor chips 40 to be mounted on the circuit board 4 may beselected depending on the width of the document sheet to be read by theimage scanner A.

Referring back to FIG. 6, each row NR, NG, NB of light receivingelements 41R, 41G, 41B in each image sensor chip 40 may has a pitch Pbetween the light receiving elements in the primary scanning directionN1. The pitch between the light receiving elements in the secondaryscanning direction N2 is also set to P. Each light receiving element hasa length of L in the secondary scanning direction. In the illustratedembodiment, L is equal to P/2.

Typically, each of the light receiving elements 41R, 41G, 41B maycomprise a phototransistor which is capable of providing photoelectricconversion for generating a voltage in accordance with the amount ofreceived light. The color selectivity of the phototransistor may beprovided by using a color filter.

Thus, as shown in FIG. 7, each red light receiving element 41R iscovered by a red filter 42R which allows selective permeation of redlight, whereas each green light receiving element 41G is covered by agreen filter 42G which allows selective permeation of green light.Similarly, each blue light receiving element 41B is covered by a bluefilter 42B which allows selective permeation of blue light. Each of thecolor filters 42R, 42G, 42B, which may be made of e.g., an appropriatelycolored photosensitive resin or film, is slightly larger in length andwidth than a corresponding light receiving element. As illustrated, thesurface of the chip substrate of the image sensor chip 40 is covered bya protection layer 43 which is black. The protection layer 43 is formedwith a plurality of through-holes 43a corresponding in position to thelight receiving elements 41R, 41G, 41B, respectively.

Of the three color filters, the red filter 42R has the greatestthickness. On the other hand, the green filter 42G has an intermediatethickness, while the blue filter 42B has the smallest thickness. Withsuch an arrangement, the blue filter 42B has the greatest lighttransmittance, whereas the green filter 42G has the second greatesttransmittance, and the red filter 42R has the smallest transmittance. Inthis way, the sensitivity of the respective light receiving elements canbe equalized. The specific thickness of the respective color filters maybe determined by experiment in the following manner.

First, a red-colored test chart is prepared. Then, the red test chart isread out by the image scanner A, and the level of an image signalsupplied by the light receiving element 41R is measured. Similar stepsare performed, using a green-colored test chart for the light receivingelement 41G, and a blue-colored test chart for the light receivingelement 41B. The thickness of the respective color filters is determinedso that the levels of the image signals supplied from the respectivecolor filters are the same.

The sensitivity control for the light receiving elements 41R, 41G, 41Bmay be provided in anther way. For instance, as shown in FIG. 8, thesurface areas of the light receiving elements may be rendered differentfrom each other. In the illustrated example, the length LR of theelement 41R is the smallest, while the length LG of the element 41G isthe second smallest, and the length LB of the element 41B is thegreatest. The widths of the respective elements 41R, 41G, 41B are allthe same in the illustrated example.

Reference is now made to FIG. 9 which is a block diagram illustrating acontrolling section of the image scanner A of the present invention. Thecontrol section includes a CPU (central processing unit) 101, a ROM(read-only memory) 102, a RAM (random-access memory) 103, and an I/O•IF(input/output interface) 104. The CPU 101 includes a timing controller101a and a signal selector 101b.

The CPU 101 provides an overall control of the image scanner A as awhole. The ROM 102 stores various programs or the like as required foroperating the CPU 101. The RAM 103 provides a working area for the CPU101 while also storing digital data such as image data and the like. TheI/O interface 104 functions for the CPU 101 for data transmission toand/or from the image sensor chips 40, the inverter 3, and a motor 105.The I/O interface 104 also serves to convert analog image signals intodigital image signals. The motor 105 is used to actuate rollers (notshown) for transferring document sheets in the secondary scanningdirection.

Each of the image sensor chips 40 has a photoelectric conversion circuitfor its operation, as shown in FIG. 11. More specifically, thephotoelectric conversion circuit incorporates a 128-bit shift register401, a chip selector 402, a group of red light phototransistorsPTR1-PTR128 (constituting the red light receiving elements 41R), a groupof green light phototransistors PTG1-PTG128 (constituting the greenlight receiving elements 41G), a group of blue light phototransistorsPTB1-PTB128 (constituting the blue light receiving elements 41B), agroup of first red light field-effect transistors FETR1-FETR128, a groupof first green light field-effect transistors FETG1-FETG128, a group offirst blue light field-effect transistors FETB1-FETB128, a second redlight field-effect transistor FETR201, a second green light field-effecttransistor FETG201, a second blue light field-effect transistor FETB201,a third red light field-effect transistor FETR211, a third green lightfield-effect transistor FETG211, a third blue light field-effecttransistor FETB211, a red light operation amplifier OPR1, a green lightoperation amplifier OPG1, a blue light operation amplifier OPB1, a groupof three red light resistors RR1-RR3, a group of three green lightresistors RG1-RG3, a group of three blue light resistors RB1-RB3, andeleven terminal pads SI, CLK, GND, AOR1, AOR2, SO, AOG1, AOG2, AOB1,AOB2, VDD. Each of the first field-effect transistors FETR1-FETR128,FETG1-FETG128, FETB1-FETB128, the second field-effect transistorsFETR201, FETG201, FETB201 and the third field-effect transistorsFETR211, FETG211, FETB211 may be a MOS (metal oxide semiconductor)field-effect transistor.

Selected ones of the pads SI, CLK, GND, AOR1, AOR2, SO, AOG1, AOG2,AOB1, AOB2, VDD are connected to an external circuitry (not shown)through the connector 49 (see FIG. 1). The pad SI receives serial-insignals. The pad CLK is fed with clock signals of e.g., 8 MHz. The padGND is used for grounding purposes. The pad AOR1 outputs a non-amplifiedanalog image signal corresponding to the received amount of red light,whereas the pad AOR2 outputs an amplified red image signal. The pad AOG1outputs a non-amplified analog image signal corresponding to thereceived amount of green light, whereas the pad AOG2 outputs anamplified green image signal. The pad AOB1 outputs a non-amplifiedanalog image signal corresponding to the received amount of blue light,whereas the pad AOB2 outputs an amplified blue image signal. The pad SOoutputs serial-out signals. The pad VDD is supplied with a logic powervoltage of 5 volts for example.

Next, description is made to an example of using the image scanner A toperform image reading.

First, a document sheet K is advanced on the glass plate 9, and thecold-cathode tube 2 is turned on to generate white light for irradiatingthe document sheet K. The white light reflected on the document sheet Kis collected by the lens array 7 for focusing on the array of imagesensor chips 40, thereby forming a non-inverted, non-magnified image atthe respective rows of light receiving elements 41R, 41G, 41B.

In accordance with the received amount of light, the light receivingelements 41R, 41G, 41B generate electric signals. More specifically,under the control of the timing controller 101a of the CPU 101, thelight receiving elements 41R, 41G, 41B output a first group of imagesignals for one scanning line while the document sheet K is advanced bya distance of (P-L). Then, under the control of the timing controller101a again, the light receiving elements 41R, 41G, 41B output a secondgroup of image signals for the same scanning line while the documentsheet K is advanced by an additional distance of L.

According to the illustrated embodiment, the image signals of the firstgroup are stored in the RAM 103 as necessary signals under the controlof the signal selector 101b of the CPU 101, whereas the image signals ofthe second group are ignored or discarded as unnecessary image signals.Alternatively, however, the image signals in the first portion may beignored, whereas the image signals in the second portion may be storedin the RAM 103 for further processing.

It should be appreciated that while the document sheet K is advanced bya distance of (P-L), the light receiving elements 41R, 41G, 41B willscan the document sheet K by a distance of P in the second scanningdirection. Thus, by ignoring the image signals of the second group, asdescribed above, it is possible to perform image reading for eachscanning line in a non-overlapping manner as viewed in the secondaryscanning direction.

In this regard, reference is made to FIG. 10, wherein T represents atime taken for the document sheet K to be advanced by the distance P.Red light image signals generated by the light receiving elements 41Rduring the first half of T are designated by Rn, Rn+1, Rn+2 and soforth, while red light image signals generated by the same elements 41Rduring the second half of T are designated by Rn', Rn+1', Rn+2', and soforth. Similarly, green light image signals generated by the lightreceiving elements 41G during the first half of T are designated byGn-1, Gn, Gn+1 and so forth, while green light image signals generatedby the same elements 41G during the second half of T are designated byGn-1', Gn', Gn+1' and so forth. Further, blue light image signalsgenerated by the light receiving elements 41B during the first half of Tare designated by Bn-2, Bn-1, Bn and so forth, while blue light imagesignals generated by the same elements 41B during the second half of Tare designated by Bn-2', Bn-1', Bn' and so forth.

According to the present invention, the image signals Rn, Rn+1, Rn+2, .. . ,Gn-1, Gn, Gn+1, . . . ,Bn-2, Bn-1, Bn, . . . (the first group ofimage signals) are adopted as necessary signals, while the image signalsRn', Rn+1', Rn+2', . . . ,Gn-1', Gn', Gn+1', . . . ,Bn-2', Bn-1', Bn', .. . (the second group of image signals) are ignored by the CPU 101.

Next, description is made to operational details of the image sensorchips 40.

Image reading by the image scanner A takes place serially orsuccessively from one image sensor chip 40 to the next in the array.Specifically, for example, the serial image reading starts from theleft-end image sensor chip 40 (first image sensor chip) in the arrayshown in FIG. 1 and ends at the right-end image sensor chip (last imagesensor chip). The image reading process in each of the image sensorchips 40 is performed in the following manner.

While clock signals of e.g., 8 MHz are input to the pad CLK, serial-insignals are supplied to the pad SI. The serial-in signals thus suppliedare input to a set terminal of the chip selector 402. As a result, thechip selector 402 outputs high-level select signals from a select-outterminals in synchronism with the clock signals. The high-level selectsignals, which are obtained by inverting the clock signals, are theninput to the respective gates of the second field-effect transistorsFETR201, FETG201, FETB201, thereby causing these transistors to turn onwhile the clock signals are held at the low level.

On the other hand, the serial-in signals are also supplied to aserial-in terminal of the shift register 401 in synchronism with theclock signals which are input to a clock terminal of the shift register401. When a serial-in signal is input to the first bit of the shiftregister 401 in synchronism with the drop of a clock signal, the firstbit becomes ON to feed a high-level signal to the respective gates ofthe first field-effect transistors FETR1, FETG1, FETB1 (corresponding tothe first bit of the shift register 401), thereby causing thesetransistors to turn on. At this time, since the clock signal is at thelow level, the respective third field-effect transistors FETR211,FETG211, FETB211 receiving the clock signal without inversion are heldOFF. As a result, a current passes through the respective resistors PR3,PG3, PB3 due to the charge which is accumulated at the respectivephototransistors PTR1, PTG1, PTB1 and discharged through the relevantfirst field-effect transistors FETR1, FETG1, FETB1. The voltage acrossthe respective resistors PR3, PG3, PB3 is input to the non-invertingterminal of the respective operation amplifiers OPR1, OPG1, OPB1 andthereby amplified with an amplification factor which is determined bythe resistance ratio between a respective one of the resistors PR1, PG1,PB1 and a respective one of the resistors PR2, PG2, PB2. The amplifiedvoltage thus obtained is output from the respective pads AOR2, AOG2,AOB2 through the respective second field-effect transistors FETR201,FETG201, FETB201 which are held ON while the clock signal is held at thelow level, i.e., while the select signal is held at the high level. Atthe same time, the non-amplified voltage across the respective resistorsPR3, PG3, PB3 is output from the respective pads AOR1, AOG1, AOB1.

Conversely, when the clock signal rises from the low level to the highlevel, the respective second field-effect transistors FETR201, FETG201,FETB201 turn off, but the respective third field-effect transistorsFETR211, FETG211, FETB211 turn on. As a result, no output is availablefrom the respective pads AOR2, AOG2, AOB2, and the remaining charge ofthe respective phototransistors PTR1, PTG1, PTBl is discharged throughthe respective first field-effect transistors FETR1, FETG1, FETB1 andthe respective third field-effect transistors FETR211, FETG211,FET13211. When the clock signal subsequently drops again from the highlevel to the low level, the serial-in signal previously held at thefirst bit of the shift register 401 is shifted to the second bit to turnon the respective first field-effect transistors FETR2, FETG2, FETB2corresponding to the second bit, and the respective second field-effecttransistors FETR201, FETG201, FETB201 turn on. As a result, the chargeof the respective second-bit phototransistors PTR2, PTG2, PTB2 isdischarged through the relevant first field-effect transistors FETR2,FETG2, FETB2, thereby generating a voltage across the respectiveresistors PR3, PG3, PB3. The voltage thus generated is output from therespective pads AOR1, AOG1, AOB1 without amplification as well as fromthe respective pads AOR2, AOG2, AOB2 after amplification at therespective amplifiers OPR1, OPG1, OPB1.

By repeating the above steps, the other phototransistors PTR3-PTR128,PTG3-PTG128, PTB3-PTB128 of the same image sensor chip 40 (the firstimage sensor chip) for the respective colors (red, green and blue) maybe successively scanned for output of non-amplified image signals fromthe respective pads AOR1, AOG1, AOB1 while also outputting amplifiedimage signals from the respective pads AOR2, AOG2, AOB2. When theserial-in signal is output from the last bit of the shift register 401at a relevant drop of the clock signal, the serial-in signal is input toa clear terminal of the chip selector 402 while also being taken out asa serial-out signal from the pad SO. As a result, the chip selector 402of the first image sensor chip 40 keeps the select signal at the lowlevel.

The serial-out signal from the pad SO of the first image sensor chip 40(the left-end image sensor chip in FIG. 1) is input to the pad SI of thenext image sensor chip 40 (second image sensor chip) as a serial-insignal. This causes the second image sensor chip 40 to operate in thesame way as the first image sensor chip.

The third and any subsequent image sensor chips 40 operate successivelyin the same manner as the first and second image sensor chips.

The analog image signals (for the respective colors) from the right-endimage sensor chip or last image sensor chip are converted into digitalsignals by the I/O interface 104 to be stored in the RAM 103. Here, itshould be noted that the digital signals to be stored in the RAM 103 areobtained while the document sheet K is being advanced by a distance of(P-L).

On the other hand, in the illustrated embodiment, the image signalsgenerated by the respective light receiving elements during the secondhalf of T are ignored by the signal selector 101b of the CPU 101.

In the embodiment described above, the CPU 101 (or the signal selector101b thereof) selects the necessary image signals to be stored in theRAM 103. Alternatively, the selection may be performed by the I/Ointerface 104. In this case, the selection. may be made by convertingonly the necessary analog signals into digital signals while theunnecessary image signals are not converted into digital signals.

According to the present invention, it is also possible to arrange thatnecessary image signals for each scanning line are output from the lightreceiving elements 41R, 41G, 41B while the document sheet K is beingadvanced by a distance which is slightly smaller than (P-L).

Reference is now made to FIGS. 12 and 13 which illustrate a secondembodiment of the present invention. In this embodiment, the CPU 101includes an output timing controller 101a as in the first embodiment,and a light controller 101c, as shown in FIG. 12. For a light source,use may be made to an LED (light-emitting diode) capable of emittingwhite light.

According to the second embodiment, under the control of the lightcontroller 101c, the light source is turned on while the document sheetK is being advanced by a distance α while the light is turned off whilethe document sheet K is being advanced by another distance β. Here, α isno greater than (P-L), and (α+β) is equal to P. As is illustrated, thelight is turned on again while the document sheet K is being advanced byanother distance α, and turned off again while the document sheet K isbeing advanced by another distance β.

In the above embodiment, under the control of the output timingcontroller 101a, each of the light receiving elements outputs an imagesignal when the light source is turned off.

The preferred embodiments of the present invention being thus described,it is obvious that the same may be varied in various ways.

For instance, the sensitivity control for the light receiving elementsmay be performed by adjusting the amplification factors of the operationamplifiers OPR1, OPG1, OPB1. In this case, the amplification factor ofthe operation amplifier OPR1 may be the smallest, the amplificationfactor of the operation amplifier OPG1 may be the second smallest, andthe amplification factor of the operation amplifier OPB1 may be thegreatest.

Further, the sensitivity control for the light receiving elements may beperformed by adjusting the luminance of components (red, green and blue)of white light generated by the cold-cathode tube. Specifically, theluminance of the blue component may be rendered the greatest, theluminance of the green component may be rendered the second greatest,and the luminance of the red component may be rendered the smallest.

Such variations should not be regarded as a departure from the spiritand scope of the invention, and all such variations as would be obviousto those skilled in the art are intended to be included within the scopeof the appended claims.

What is claimed is:
 1. An image reading apparatus comprising:a lightsource for irradiating a document sheet with light; a row of red lightreceiving elements arranged in a primary scanning direction fordetecting a red component of the light reflected on the document sheet,each red light receiving element having a length of L in a secondaryscanning direction which is perpendicular to the primary scanningdirection; a row of green light receiving elements arranged in theprimary scanning direction for detecting a green component of thereflected light, the row of green light receiving elements beingdisplaced from the row of red light receiving elements by a distance ofP in the secondary scanning direction, each green light receivingelement having a length of L in the secondary scanning direction; a rowof blue light receiving elements arranged in the primary scanningdirection for detecting a blue component of the reflected light, the rowof blue light receiving elements being displaced from the row of greenlight receiving elements by a distance of P in the secondary scanningdirection, each blue light receiving element having a length of L in thesecondary scanning direction; and a signal selector; wherein, inperforming image reading for one scanning line, the signal selector isarranged to adopt, as a necessary image signal, a voltage generated byeach of the light receiving elements during a period when said eachlight receiving element is moved in the secondary scanning directionrelative to the document sheet by a first feed distance, the signalselector being also arranged to disregard, as an unnecessary imagesignal, a voltage generated by said each light receiving element duringa period when said each light receiving element is moved in thesecondary scanning direction relative to the document sheet by a secondfeed distance subsequent to the first feed distance.
 2. The imagereading apparatus according to claim 1, wherein the first feed distanceis equal to (P-L), the second feed distance being equal to L.
 3. Theimage reading apparatus according to claim 2, wherein L is equal to P/2.4. The image reading apparatus according to claim 1, wherein the firstfeed distance is smaller than (P-L), the second feed distance beinggreater than L.
 5. The image reading apparatus according to claim 1,wherein the light source comprises a cold-cathode tube.
 6. The imagereading apparatus according to claim 1, wherein the light sourcecomprises a light-emitting diode.
 7. An image reading apparatuscomprising:a light source for irradiating a document sheet with light; arow of red light receiving elements arranged in a primary scanningdirection for detecting a red component of the light reflected on thedocument sheet, each red light receiving element having a length of L ina secondary scanning direction which is perpendicular to the primaryscanning direction; a row of green light receiving elements arranged inthe primary scanning direction for detecting a green component of thereflected light, the row of green light receiving elements beingdisplaced from the row of red light receiving elements by a distance ofP in the secondary scanning direction, each green light receivingelement having a length of L in the secondary scanning direction; a rowof blue light receiving elements arranged in the primary scanningdirection for detecting a blue component of the reflected light, the rowof blue light receiving elements being displaced from the row of greenlight receiving elements by a distance of P in the secondary scanningdirection, each blue light receiving element having a length of L in thesecondary scanning direction; a light controller; wherein, in performingimage reading for one scanning line, the light controller is arranged toturn on the light source during a period when each of the lightreceiving elements is moved in the secondary scanning direction relativeto the document sheet by a first feed distance, the light controllerbeing also arranged to turn off the light source during a period whensaid each light receiving element is moved in the secondary scanningdirection relative to the document sheet by a second feed distancesubsequent to the first feed distance.
 8. The image reading apparatusaccording to claim 7, wherein the first feed distance is equal to (P-L),the second feed distance being equal to L.
 9. The image readingapparatus according to claim 7, further comprising an output timingcontroller for regulating output of an image signal from each of thelight receiving elements, so that the image signal is output from saideach light receiving element when the light source is turned off.